1. Field of the Invention
The present invention relates to an image pickup apparatus suitable for use in a video camera which has a mode for photographing a subject located at a predetermined distance and is equipped with an adapter for holding a film original at the predetermined distance so that the film original is photographed, and, more specifically, to lens control in the image pickup apparatus.
2. Description of Related Art
With rapid technical improvements in personal computers and peripherals, it has been becoming easier for photographers to store, for example, photographs taken with cameras using silver-halide film in memories of personal computers and edit the stored photographs to create their original picture postcards or posters, and the demand for the field of such art has been becoming greater in markets year after year.
To input a photograph to a personal computer, it is necessary to convert image information of a photograph into an electrical signal by using a video camera, so that a device for fixing the position of a subject such as a photograph becomes necessary. Since photographs are printed on printing paper in variously different sizes, an awkward operation is needed to set a field angle and correct lighting for each photograph. It is also necessary to prepare a large-sized dedicated image pickup apparatus having a fixing base for a video camera.
FIG. 1 shows a manner in which a negative film 901 held in a film holder 902 is photographed by using a VTR-integrated type camera 904 with a film adapter 903 attached thereto. The negative film;901 is illuminated from its rear side by a backlight (not shown) provided in the film adapter 903, and a transmitted image is photographed by the VTR-integrated type camera 904. If the VTR-integrated type camera 904 has the function of converting a negative image into a positive image (a negative/positive conversion function), the electrical signal outputted from the VTR-integrated type camera 904 is a video signal indicative of a positive image even during the photography of the negative film 901. If this video signal is inputted to a personal computer 905, the positive image can be stored in a memory provided in the personal computer 905. In the method shown in FIG. 1, since the size of each frame of the negative film 901 is uniform and only the backlight can be used as a light source, a photographic image can be stored in the personal computer 905 far more readily than when an image of a photograph printed on printing paper is picked up.
FIG. 2 shows a lens system called an inner focus type lens system, which includes a fixed first lens group 102, a variator lens 103, an iris 104, a fixed third lens group 105 and a focusing/compensating lens 106. Reference numeral 107 denotes an image pickup element such as a CCD, the image pickup surface of which is shown in FIG. 2.
FIG. 3 shows the image pickup surface in-focus position of the focusing/compensating lens 106 with respect to the subject distance for leach focal length. In FIG. 3, the horizontal axis represents the position of the variator lens 103, while the vertical axis represents the position of the focusing/compensating lens 106. As can be seen from FIG. 3, in the lens system shown in FIG. 2, if the focusing/compensating lens 106 is moved to focus an image on the image pickup element 107, the position of the focusing/compensating lens 106 with respect to the subject distance varies for each local length. It is known that when the variator lens 103 is on a shortest focal length side, if the focusing/compensating lens 106 is moved to the vicinity of its closest-distance end, a minimum subject distance which can be focused by the focusing/compensating lens 106 is reduced to an immediately close distance from the first lens group 102. In FIG. 3, a curve 601 represents an in-focus curve relative to an extremely short subject distance which is several centimeters to the first lens group 102, and it can be seen from FIG. 3 that the lens-focusable focal length area of the variator lens 103 with respect to this subject distance is a limited area 602 which extends from the wide-angle end to a point A on a short focal length side. Accordingly, if an in-focus image is to be obtained on the image pickup element 107 when a film lying at an extremely close distance from the fixed first lens group 102 is being photographed by using the film adapter 903 shown in FIG. 1, the combination of the positions of the variator lens 103 and the focusing/compensating lens 106 must be contained in a portion 604 defined by three areas 601, 602 and 603 in FIG. 3.
A method of maintaining an in-focus state during zooming in the inner focus type lens system will be described below. In FIG. 3, the position of the focusing/compensating lens 106 for focusing an image on the image pickup element 107 is continuously plotted with respect to different subject distances for each focal length. During zooming, a cam locus is selected from among the loci of FIG. 3 according to the subject distance, and if the focusing/compensating lens 106 is moved along the selected cam locus, zooming free of defocusing can be effected.
FIG. 4 is a view aiding in describing one example of a locus tracing method which has previously been proposed. In FIG. 4, Z0, Z1, Z2, . . . , Z6 indicate the position of a variator lens, a0, a1, a2, . . . , a6 and b0, b1, b2, . . . , b6 respectively indicate representative loci stored in a lens control microcomputer, and p0, p1, p2, . . . , p6 indicate a locus calculated on the basis of the two loci. An equation for calculating this locus is shown below:
p(n+1)=(|p(n)xe2x88x92a(n)|/|b(n)xe2x88x92a(n)|)xc3x97|b(n+1)xe2x88x92a(n+1)|+a(n+1).xe2x80x83xe2x80x83(1)
According to Equation (1), for example, if a focusing/compensating lens is located at the point p0 in FIG. 4, the ratio in which the point p0 internally divides a line segment b0xe2x88x92a0 is obtained, and a point which internally divides a line segment b1xe2x88x92a1 in accordance with that ratio is determined as p1. The moving speed of the focusing/compensating lens required to keep an in-focus state can be found from the p1xe2x88x92p0 positional difference and the time required for the variator lens to move from Z0 to Z1.
A case in which the stop position of the variator lens is not limited only to boundaries having stored representative locus data will be described below with reference to FIG. 5. FIG. 5 is a view aiding in describing a method for interpolating the position of the variator lens. FIG. 5 is an extracted portion of FIG. 4 and shows a case in which the variator lens can be stopped at an arbitrary stop position.
In FIG. 5, the vertical and horizontal axes respectively represent the position of the focusing/compensating lens and the position of the variator lens. Letting Z0, Z1, . . . , Zkxe2x88x921, Zk, . . . Zn represent the position of the variator lens, the corresponding positions of the focusing/compensating lens for different subject distances, i.e., the representative locus positions (the position of the focusing/compensating lens relative to the position of the variator lens) stored in the lens control microcomputer are as follows:
a0, a1, . . . , akxe2x88x921, ak, . . . an,
b0, b1, . . . , bkxe2x88x921, bk, . . . bn.
If it is now assumed that the position of the variator lens is Zx which is not a zoom boundary position and that the position of the focusing/compensating lens is px, positions ax and bx are obtained as follows:
ax=akxe2x88x92(Zkxe2x88x92Zx)xc3x97(akxe2x88x92akxe2x88x921)/(Zkxe2x88x92Zkxe2x88x921),xe2x80x83xe2x80x83(2)
bx=bkxe2x88x92(Zkxe2x88x92Zx)xc3x97(bkxe2x88x92bkxe2x88x921)/(Zkxe2x88x92Zkxe2x88x921).xe2x80x83xe2x80x83(3)
Specifically, in accordance with an internal ratio which is obtained from the current position of the variator lens and two adjacent opposite zoom boundary positions (for example, Zk and Zkxe2x88x921 in FIG. 5), locus data corresponding to the same subject distance are selected from among four stored representative locus data (ak, akxe2x88x921, bk, bkxe2x88x921 in FIG. 5) and are internally divided by the internal ratio shown by the above equation (1), whereby ax and bx can be obtained.
Then, in accordance with an internal ratio which is obtained from ax, px and bx, the locus data corresponding to the same focal length, which are selected from among the four stored representative locus data (ak, akxe2x88x921, bk, bkxe2x88x921 in FIG. 5), are internally divided by the internal ratio shown by the above equation (1), whereby pk and pkxe2x88x921 can be obtained. Furthermore, during zooming from the wide-angle end toward the telephoto end, the moving speed of the focusing/compensating lens required to keep an in-focus state can be found from the difference between the target focus position pk and the current focus position px and the time required for the variator lens to move from Zx to Zk. Furthermore, during zooming from the telephoto end toward the wide-angle end, the moving speed of the focusing/compensating lens required to keep an in-focus state can be found from the difference between the target focus position pkxe2x88x921 and the current focus position px and the time required for the variator lens to move from Zx to Zkxe2x88x921. The above-described locus tracing method has been devised.
However, the above-described conventional example has the problem that if a negative film or a slide film is to be photographed by using a film adapter or the like, a lens-nonfocusable focal length area occurs, and if the film adapter is attached when the, variator lens is in such area, the subject cannot be focused and is placed in a greatly defocused state.
In addition, an automatic focus adjustment (AF) operation, if it is similar in operational characteristic to that during normal photography, offers the problem of causing a malfunction during photography using a film adapter or the like. For example, the essential portion of a subject is not always located in the center of a frame of a film, or if a film is moved to a slight extent, the AF operation may be restarted even if a subject distance does not vary.
The present invention has been made to solve the above-described problems, and its first object is to prevent a malfunction by optimizing characteristics such as zooming characteristics and AF characteristics during an image pickup operation using an accessory such as a film adapter.
A second object of the present invention is to make it possible to bring a focusing/compensating lens into focus even if a variator lens lies in a lens-nonfocusable focal length area, by forcedly moving, when photography is to be performed with a film adapter or the like, the variator lens to a lens-focusable focal length area while causing the focusing/compensating lens to trace an in-focus cam locus as accurately as possible.
To achieve the above objects, in accordance with one aspect of the present invention, there is provided an image pickup apparatus which comprises first lens means for varying a focal length and performing a magnification varying operation, second lens means for performing focus adjustment, image pickup means for picking up a subject image passing through the first and second lens means and converting the picked-up subject image into an electrical signal, setting means for setting a mode for picking up an image of a subject located at a predetermined distance, detecting means for detecting a setting of the mode, and control means for performing control for shifting an area in which the first lens means is movable during the magnification varying operation to a predetermined area when the setting of the mode is detected by the detecting means.
In accordance with another aspect of the present invention, there is provided an image pickup apparatus which comprises first lens means for varying a focal length and performing a magnification varying operation, second lens means for performing focus adjustment, image pickup means for picking up a subject image passing through the first and second lens means and converting the picked-up subject image into an electrical signal, setting means for setting a mode for picking up an image of a subject located at a predetermined distance, detecting means for detecting setting of the mode, and control means for performing control for forcedly moving the first lens means to a lens-focusable focal length area when the setting of the mode is detected by the detecting means.
A third object of the present invention is to provide an image pickup apparatus capable of automatically performing zooming free of defocusing during the attachment of a film adapter.
A fourth object of the present invention is to provide a stable and highly reliable image pickup apparatus which does not cause defocusing due to malfunction of AF nor malfunction due to movement of film during the attachment of a film adapter.
A fifth object of the present invention is to solve the above-described problems by making a wobbling amplitude larger than a normal wobbling amplitude so as to correctly determine in which direction to move a focusing/compensating lens, or by shortening a focusing time by increasing a hill-climbing speed, or by setting the amount of decrease in an AF evaluation signal value which is used for detecting whether the focusing/compensating lens has reached a peak, to a value larger than a normal amount, because there is no possibility that recording of a film, a print or the like in an out-of-focus state is performed during photography using a film adapter or the like; or by shortening the focusing time by omitting the operation of confirming through wobbling whether the focusing/compensating lens is in focus at the peak, or by increasing a restart determining time and preventing the driving of the focusing/compensating lens from being unnecessarily restarted, because panning does not occur during photography using a film adapter or the like.
A sixth object of the present invention is to provide an image pickup apparatus which does not perform an AF restart operation based on a variation in the state of a subject but performs an AF restart operation only when any key or the like is operated, because a subject distance is constant at all times when a film, a print or the like is being photographed by using a film adapter or the like.
A seventh object of the present invention is to provide an image pickup apparatus capable of enlarging an AF evaluation value acquisition area as shown in FIG. 36(b) to ensure a wider AF evaluation value acquisition area, because, when a film, a print or the like is being photographed by using a film adapter or the like, a subject distance is constant and a contention in focusing between a distant subject and a near subject need not be taken into account.
The above and other objects, features and advantages of the present invention will become apparent from the following detailed description of preferred embodiments of the present invention, taken in conjunction with the accompanying drawings.